1. Field of the Invention
The present invention relates to an electric apparatus provided with a power supply. Particularly, the present invention relates to an electric apparatus with a power supply including an electric double layer capacitor.
2. Discussion of Background
When electric apparatuses are classified from the consumption pattern of electric power, there are constant load type electric apparatuses which consume continuously a relatively constant electric power and peak load type electric apparatuses which consume intermittently a relatively large electric power. The constant load type electric apparatuses include electric devices such as desk lamps, flashlights, personal computers, wordprocessors, portable telephones and cordless telephones, which consume electric power at a relatively constant rate during use.
On the other hand, the peak load type electric apparatuses are electric devices such as electric screw drivers, electric drills, electric spot welding machines, electric cars and electric scooters which require a large electric power for a short time. These apparatuses consume intermittently a relatively large electric power during use, in other words, they consume a high peak power of a short duration repeatedly with certain time intervals.
In either type of the electric apparatuses, power sources, such as commercial a.c. power lines, batteries, solar cells or the like are used. In some cases, generators specially designed for the purpose are used.
When the electric power is to be obtained from commercial a.c. power lines, it is inconvenient because one cannot be freed from the cable.
On the other hand, when a battery is used as a power source, the apparatus can be carried around without a cable. In particular, a secondary battery is advantageous for it can store the energy and does not require any sunlight as in the case of a solar cell.
However, the secondary battery has a serious problem that it takes long time for charging, and it is common that the time required for charging is longer than the time of use. Further, from the nature of the secondary batteries, it is difficult to utilize the full capacity, i.e. charging and discharging to 100% of the capacity is almost impossible.
The secondary battery has a further restriction that the service life (cycle life) will shortly be expired by repeated charge and discharge. There is a tendency of reducing the service life as the charging time is shortened by increasing the charge current or as the energy density of a battery is increased.
Japanese Unexamined Patent Publication No. 161280/1993 discloses an auxiliary power supply for a vehicle provided with an electric double layer capacitor having a large capacitance in addition to a battery (a secondary battery). The auxiliary power supply is so adapted that an output power of regenerative braking from a retarder at the time of braking of the vehicle is stored in the capacitor through a rectifier, and the battery is charged with energy stored in the capacitor as required.
Although the electric double layer capacitor can effectively store electric power from the retarder even if the power is large and intermittent, there is a problem of charging deficiency when the battery is charged with electric power from the capacitor.